Many devices for the reception and restitution of audiovisual content are configured to enable the local recording to an item of audiovisual content and its subsequent restitution at reception. These devices are frequently equipped with recording modules, such as hard drives, or flash memory modules featuring read and write functions equivalent to those of a hard drive storage unit.
The users of such a device can then view an item of recorded audiovisual content at any time whenever they like and have time.
Sometimes a user thinks he has time to view an item of audiovisual content, begins to watch it, and then if there is not enough time, wants to watch it in an accelerated manner.
Methods exist that allow content to be viewed in an accelerated manner, without degrading the restitution quality, that is to say without the user perceiving an accelerated display effect and without the audio component being deformed by the restitution occurring in a shorter time period than its native duration.
These techniques remove some images, cleverly distributed over time with regard to the video, and use techniques specific to accelerated audio restitution with regard to the audio.
Today it is possible, with some reception, recording, and restitution equipment, to view an hour of audiovisual content in 40 minutes, for example.
With regard to the rapid restitution of audio, that is to say in a shorter duration than its nominal duration, it is possible to categorize the techniques used into three ways to operate.
A first technique consists of reading the audio component of a content at the same speed at the video component, which generates a tone distortion relative to the encoded audio component. The acceleration shifts the audio restitution to a higher pitch.
This first technique is deemed to be unacceptable from a business perspective because it leads to an overly degraded quality of restitution.
A second technique consists of applying processing to the encoded audio component, such that, during the quick restitution, there is no alteration in the tone. This is the case, for example, when the audio component is restituted more quickly and frequency transpositions are applied to the audio samples.
This second technique produces acceptable results in terms of audio restitution quality, but because of all the processing to be carried out, it requires substantial processor and memory resources, which is disadvantageous from the viewpoint of system load, particularly in a real-time multitasking environment.
A third technique consists of accelerating the audio restitution, while removing pieces of the audio frames that make up the audio components. This method corresponds, for example, to the known processing that uses the WSOLA (“Waveform-similarity-based Synchronised OverLap-Add”) algorithm.
This third technique achieves satisfactory results, like the previous one, but it still requires lots of resources when the reception and restitution device operates at the limit of its processor and memory resources.